Bifidobacterium lactis is a probiotic bacterium commonly included in supplements aimed at supporting gut health, including conditions like Leaky Gut Syndrome (increased intestinal permeability). The scientific evidence supporting its use for Leaky Gut Syndrome is modest but emerging. Several animal and in vitro studies suggest that B. lactis can enhance gut barrier function by increasing the expression of tight junction proteins and reducing inflammatory markers associated with increased permeability. For example, studies in mice have shown that supplementation with B. lactis can reduce markers of gut inflammation and help restore the integrity of the gut lining after it has been compromised by stress or infection.

In human research, the evidence is more limited. Some small clinical trials and pilot studies indicate that B. lactis-containing probiotics may help reduce symptoms associated with gut barrier dysfunction, such as bloating, abdominal pain, and stool irregularities, particularly in people with irritable bowel syndrome (IBS) or inflammatory bowel disease (IBD). However, direct studies specifically on "Leaky Gut Syndrome" as a standalone diagnosis are sparse, largely because the syndrome is not universally recognized in conventional medicine and lacks standardized diagnostic criteria.

Overall, while there is some scientific rationale and preliminary evidence for the use of B. lactis in supporting gut barrier function, high-quality, large-scale clinical trials in humans with clearly defined "leaky gut" are still needed. At present, the evidence is promising but not definitive, warranting a modest evidence rating.